1. Field of the Invention
The present invention relates to a material for making a pattern for use in investment casting in which the pattern is formed by wax, then coated with a refractory layer to build an investment shell mold.
2. Description of the Related Art
Investment casting is a casting technique in which a pattern is formed from wax injected into die, then coated repeatedly with a refractory layer, to build a shell around the wax pattern. Then the wax is melted and run out, and the refractory shell of the mold is strengthened by heating. Thereafter at the elevated temperature, the mold is filled with molten metal. The investment casting or the lost wax casting has several types, such as a solid mold method and a ceramic shell mold method. The ceramic shell mold is now one of the most widely used method.
The wax used in the investment casting must meet the following requirements:
(1) It melts around 50 to 70, and after it is formed in the mold, it solidifies as quickly as possible with minimum contraction;
(2) It is resistant to breakage, or withstands an external force applied thereto;
(3) It has a smooth surface, and allows a ceramic slurry to adhere thereto;
(4) It has a low viscosity when melted, and is easy to be released from mold after formed; and
(5) When burnt, no ash content therein remains.
In order to increase the working efficiency of the investment casting, particularly the ceramic shell mold method, it is essential to improve the characteristics specified in the paragraphs (1) and (2) without spoiling the qualities of the paragraphs (3), (4) and (5).
To improve the characteristics of the paragraph (1) it is preferred to use a suitable filler. However, the filler must not be resolved in the melting wax, and has a high melting point, and when burnt, leaves no ash content. To meet these requirements the filler is selected from organic compounds, such as isophthalic acid, terephthalic acid, bisphenol, phthalimide, and stearilbisamide.
However the wettability of these organic compounds with wax is not always good, and they are only effective in reducing the amount of soluble contents of the wax, and minimizing a possible contraction thereof when it solidifies.